The HEX is an over-priced tourist trap and I refuse to pay those insane HEX fares.
I just use the Piccadilly tube line to get between LHR & King's Cross. Takes ~50mins but at least it's direct and only costs £5.60 each way.
There is a hack to get that down to £3.40 if you really want to but it means you have to get off, tap out, tap back in and wait for the next train at Hatton Cross in either direction.
I just checked the TFL website and doing the same journey using HEX & Elizabeth line would cost me £27.70
each way and will only save me ~15-20mins
. No thank you.
I don't know about the West coast line, but LNER run trains every 30mins or so between King's Cross and Leeds where I then change and get a Northern Rail service to Skipton.